This invention relates to semiconductor devices which include deposited metal layers.
Among the devices to which this invention applies are monolithic integrated circuit devices of the type which include a body of semiconductor material having an insulating coating with portions of different thickness and deposited metal conductors on and adhered to the insulating coating. One such device is an MOS integrated circuit device which employs plurality of insulated gate field effect transistors with a relatively thin insulator in the gate areas of the transistors and a relatively thick insulating coating in the areas surrounding the transistors.
The purpose of the thick insulating coating in known integrated circuit devices is to reduce the capacitance interaction between the deposited conductors and the adjacent regions of the semiconductor body. This improves the speed of the circuit and reduces the changes of leakage due to parasitic inversion layers at the surface of the semiconductor body.
A significant yield loss problem has heretofore limited the maximum thickness difference between the thin and thick insulator layers. As this difference, or step height is made greater, the probability of open circuits due to breaks in the metal conductors at the steps increases. Past attempts to overcome this problem have not been commercially successful. One known approach has been to establish a sloped riser surface joining the thick and thin insulating coatings. This may be accomplished, for example, by growing an oxide coating the density of which is graded from relatively high adjacent to the semiconductor to relatively low at the free surface of the coating. When such an oxide is etched, it etches faster at the free surface than at the side adjacent to the semiconductor and consequently a surface of relatively gradual slope is achieved. An insulating coating of graded density is, however, difficult to produce.